1. Field of the Invention
The present invention relates to magnetic tape heads, and more particularly, to a planar servo write head for flexible magnetic storage media.
2. Background Information
Linear recording media, such as magnetic tapes, store data on linear data tracks that run parallel to each other over the length of the media. The magnetic media, or tape, is moved across a magnetic tape head for reading data stored on the tape and writing data to the tape. For throughput, tape heads write eight or more tracks simultaneously.
As the tape runs transversely across the magnetic tape head, the tape may move laterally relative to the head. This lateral movement of the tape may result in the head reading or writing data off track or on the wrong track. Thus, accurate positioning of the tape head relative to the tape is critical.
To enable accurate positioning of the tape head, media manufacturers may write servo tracks on the magnetic tape parallel to the data tracks. Servo readers in the tape head read the servo information in the servo tracks. The servo information is then used for aligning transducers in the head with data tracks on the tape. The servo information is also used for deriving tape velocity and for data channel timing recovery. The servo information may also include the longitudinal position of the tape, manufacturers' data, and servo-band or data-band identification. This additional data is typically encoded using phase modulation.
Servo tracks are typically written to the magnetic tape during manufacture of the tape by heads, known as servo write heads, that are dedicated to writing servo patterns. An exemplary prior art servo write head 100 is shown in FIG. 1 of the drawings. The servo write head 100 may be constructed from two blocks 102, 104 that typically comprise magnetic ferrite. The blocks may be separated by a glass spacer 106 and are bonded to the spacer. The head 100 is then lapped to form a top surface 108 of a desired contour.
A magnetic seed layer 110 is then deposited on the top surface 108. A photoresist layer may then be deposited on the seed layer 110 and patterned to form the desired write gaps 112. The fabrication techniques and processes used to fabricate known servo write heads limits minimum achievable write gaps to approximately 0.5 to 1 micrometers.
As data track density on magnetic tape increases, data track width decreases. Track following errors must also decrease. Thus, increasing servo pattern linear density is required. Resultantly, write gap widths from about 0.5 to 1 micrometers are too large for future servo pattern writing requirements due to narrower data tracks.
After the write gaps are formed, a layer of magnetic material several microns thick 114 is plated on the seed layer 110, with the write gaps extending though the magnetic layer. A wear-resistant overcoat may be deposited over the magnetic layer.
A coil 116 is wound around one of the blocks through a slot 118 that passes though the head. The coil typically has one to three coil turns that wind about the block. Electrical current is applied to the coil to create a magnetic field in the write gaps of the head. Several amperes of current are applied to the coil to generate enough magnetic field to write the servo patterns. The magnetic field sets the magnetization in the tape as it runs across the tape bearing surface, thus writing the servo patterns on the tape.
A disadvantage of the prior art head is that the large yoke structure has a very large inductance “L”. Since the response time of the head is L/r, where “r” is the series resistance, the larger inductance creates a longer rise time. Long rise time limits how fast the tape can be moved during servo pattern writing. This limits the speed that servo patterns can be written to the tape, limiting manufacturing speed of the tape. The inductance itself is proportional to N2, where N is the number of coil turns of the head. Thus, to keep inductance down, N is limited to one to three coil turns. However, this results in a requirement for larger currents flowing through the coil.
Accordingly, there is a clearly-felt need in the art for a servo write head that provides faster servo pattern writing and faster tape manufacturing speed, and has write gaps of a reduced width. These unresolved problems and deficiencies are clearly felt in the art and are solved by this invention in the manner described below.